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Monday, June 14, 2010

Above Board: Manhattan-izing an SMT kit

A while back, Tony Parks very kindly sent me one of his wonderful Softrock RXTX V6.3 Software Defined Radio kits. I took a shot at it, but it turns out that I'm not very good with surface mount construction using small parts. I've gotten very used to the Manhattan style. Still, I did manage to build one of the Power Amplifier modules, and I put it to good use in a DSB WSPR transceiver I've been building (see above) . It worked great. For a while... Then it released some smoke.

I started trouble shooting and it was at this point that I REALLY began to miss good ole' Manhattan (you see, I was born there, and I went to Manhattan College, so I guess this helps explain the affinity). It was difficult to get to components mounted under the board. The whole thing was the size of my thumb... I know, whine, whine, whine... Luddite Geezer-ism strikes again. SPARK FOREVER!

It turns out that the problem was caused by the fact that my shack is just not well suited for this kind of construction. There is a lot of stuff floating around. Conductive stuff. Look closely at the picture below and you will see what I mean. You will see what caused the release of the smoke. Look at the leads on the PA transistor on the left. That's a little bit of stray wire that found its way to the WRONG place. Note the toasted source resistor just below!

Anyway, after a trying to fix this thing, I finally gave up and decided to use the circuit, but in Manhattan form. Everything up top. No SMT. Bigger coil cores. The temperature sensing circuitry went off to the right. The output transformer went off to the left, and the driver stage went down below the kit's board. Here is what it looks like now. Again, it works great.

I want to thank Tony and the Softrock guys for giving me this experience. Their kits are wonderful and are really making a tremendous contribution to the hobby. I strongly recommend them. The instructions are great, much like those of the old Heathkits. But for me, I'll take Manhattan.

1 comment:

  1. Hi Bill

    I like retro fitting technique it
    looks realy cool.

    Tony

    ReplyDelete

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